When I'm stopped at a light the engine idles fine, but once I accelerate the car sort of sputters until it reaches a certain RPM. It only does it from a stop. It maintains speed fine. I thought maybe it could've been a dirty fuel injector so I cleaned that out, to no avail. I then noticed that the serpentine belt was wore down pretty good so I replaced that. It seemed to do the trick, but shortly afterwards it started doing the same thing. Any ideas??

You may be experiancing a secondary ingnition misfire.